It is known to designers of cylinder liners that the highest temperatures occurring in a cylinder liner are near the top of the cylinder where the liner abuts the cylinder head, and where the exhaust gasses are driven from the cylinder head through the cylinder head exhaust valves. It is also known to provide annular cooling channels in the liners at these regions of greatest heating. Some examples of the prior art in this field may be briefly described as follows.
In United Kingdom patent 392,091 to Sulzer Freres, annular cooling channels 7–9 are provided in the upper engaging portion of the cylinder liner 1 where it engages and is supported by elements surrounding it including the jacket 5 and annular ring 21. Each of the channels 7–9 is substantially less than half the axial length (height) of the upper engaging portion of the liner. Coolant from the cooling chamber 14 passes in series up through the channels 9, 8 and 7 (in that order) and is exhausted through line 15. It is to be noted that the flow capacity of this cooling system is severely limited by the in-series (as distinguished from in-parallel) nature of the flow arrangement, the cross sectional flow area in the disclosed system approaching as little as a third of what it would be were the flow arrangement parallel in nature.
In United Kingdom patent 1,525,766 to Klockner-Humboldt, annular water jacket 14 and (in the FIG. 3 embodiment) annular water jacket 19, are both within the upper engaging portion of the cylinder liner, which extends down to the guide rib 13. Coolant enters water jacket 14 from below and flows in one or the other annular direction around the illustrated but un-numbered liner channel associated with annular water jacket 14 to exhaust passage 11. If annular water jacket 19 (shown in FIG. 3 of the patent) is also provided, flow occurs through its associated liner channel in the same manner. In each case, a first path of flow to exhaust occurs though a 90-degree angular distance, and the other or second path of flow occurs through angular distance of 270 degrees. In each case, the amount of cooling water that flows through the first path exceeds that flowing through the second path due to the difference in length, and therefore of flow resistance, of the two paths. The flow channel associated with water jacket 14 extends in axial length for a distance substantially greater than half the axial length (height) of the upper engaging portion of the liner, and the flow channel associated with water jacket extends in axial length for a distance substantially less than such height.
In U.S. Pat. No. 4,926,801 to Eisenberg et al. (Eisenberg), coolant flows in parallel through annular channels. The channels have an arcuate (rather than a predominately rectilinear) shape in cross-section, and are divided from each other by ribs whose radially outer extremities are the pointed ridges 40 (referred to in the patent as “thicker portions”). These pointed ridges are intended to engage the engine block 10 in load-bearing relationship as is evident from FIG. 3 and col. 2, lines 60–64 of the specification. This arcuate and “pointy” design has disadvantages as compared to “blunt” or predominately rectilinear ribs in two respects: limited heat exchange area and high mechanical stress. In respect of limited heat-exchange area, imagine two channels that are each one unit deep and two units wide. Imagine one channel is of a rectangular shape, and the other is semi-circular. Simple geometry establishes that, with respect to the total facial area of the sides and bottom of each channel, the facial area of the rectangular channel exceeds that of the semi-circular channel by more than 27%. In Eisenberg et al., this facial-area-reducing effect is not as large due the fact that the scallops are shallower than a full semi-circle, but the effect is nevertheless significant. In respect of high mechanical stress, mechanical loading between the ridge points and the engine block 10 is through line-contact or through very narrow regions of area contact, thereby subjecting the ridge points to high mechanical stress and the possibility of early failure.
In U.S. Pat. No. 5,299,538 to Kennedy et al. (Kennedy), the main portion of coolant flowing through the cylinder block reaches an outlet port directly and without diversion, but some of the coolant is diverted into the cylinder liner and then, after flowing within and absorbing heat from the liner, is sucked back out of the liner to rejoin the main portion of coolant flow in the vicinity of an outlet port for such main portion, providing what may be referred to as “coolant shunt flow” in the liner. The coolant shunt flow occurs through a single annular cooling channel 34. When the parts are assembled, engagement of the liner and cylinder block occurs at upper cylinder block engaging portion 26, whose top extremity is the stop shoulder 28, and whose bottom extremity is a an annular diameter-reduction shoulder (no reference number) formed in the liner wall, the outer diameter of the liner wall decreasing below such shoulder. The channel 34 extends in axial length (i.e. in width) approximately half way across the upper cylinder block engaging portion 26.